CVE-2026-27738: @angular/ssr Angular SSR Has An Open Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xh43-g2fq-wjrj",
  "modified" : "2026-02-25T22:41:57Z",
  "published" : "2026-02-25T22:41:57Z",
  "aliases" : [ "CVE-2026-27738" ],
  "summary" : "Angular SSR has an Open Redirect via X-Forwarded-Prefix",
  "details" : "An Open Redirect vulnerability exists in the internal URL processing logic in Angular SSR. The logic normalizes URL segments by stripping leading slashes; however, it only removes a single leading slash.\n\nWhen an Angular SSR application is deployed behind a proxy that passes the `X-Forwarded-Prefix` header, an attacker can provide a value starting with three slashes (e.g., `///evil.com`).\n\n1. The application processes a redirect (e.g., from a router `redirectTo` or i18n locale switch).\n2. Angular receives `///evil.com` as the prefix.\n3. It strips one slash, leaving `//evil.com`.\n4. The resulting string is used in the `Location` header.\n5. Modern browsers interpret `//` as a protocol-relative URL, redirecting the user from `https://your-app.com` to `https://evil.com`.\n\n\n### Impact\nThis vulnerability allows attackers to conduct large-scale phishing and SEO hijacking:\n- **Scale:** A single request can poison a high-traffic route, impacting all users until the cache expires.\n- **SEO Poisoning:** Search engine crawlers may follow and index these malicious redirects, causing the legitimate site to be delisted or associated with malicious domains.\n- **Trust:** Because the initial URL belongs to the trusted domain, users and security tools are less likely to flag the redirect as malicious.\n\n### Attack Preconditions\n\n- The application must use Angular SSR.\n- The application must have routes that perform internal redirects.\n- The infrastructure (Reverse Proxy/CDN) must pass the `X-Forwarded-Prefix` header to the SSR process without sanitization.\n- The cache must not vary on the `X-Forwarded-Prefix` header.\n\n### Patches\n- 21.2.0-rc.1\n- 21.1.5\n- 20.3.17\n- 19.2.21\n\n### Workarounds\nUntil the patch is applied, developers should sanitize the `X-Forwarded-Prefix` header in their`server.ts` before the Angular engine processes the request:\n\n```ts\napp.use((req, res, next) => {\n  const prefix = req.headers['x-forwarded-prefix']?.trim();\n  if (prefix) {\n    // Sanitize by removing all leading slashes\n    req.headers['x-forwarded-prefix'] = prefix.replace(/^[/\\\\]+/, '/');\n  }\n  next();\n});\n\n```\n\n### Resources\n- [Report](https://github.com/angular/angular-cli/issues/32501)\n- [Fix](https://github.com/angular/angular-cli/pull/32521)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/ssr"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "21.2.0-next.0"
      }, {
        "fixed" : "21.2.0-rc.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 21.2.0-rc.0"
    }
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/ssr"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "21.0.0-next.0"
      }, {
        "fixed" : "21.1.5"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/ssr"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "20.0.0-next.0"
      }, {
        "fixed" : "20.3.17"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/ssr"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "19.0.0-next.0"
      }, {
        "fixed" : "19.2.21"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular-cli/security/advisories/GHSA-xh43-g2fq-wjrj"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27738"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular-cli/issues/32501"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular-cli/pull/32521"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular-cli/commit/f086eccc36d10cf01c426e35864bc32e1e292323"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/angular/angular-cli"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-601" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-25T22:41:57Z",
    "nvd_published_at" : "2026-02-25T17:25:40Z"
  }
}